Extremity imaging apparatus for cone beam computed tomography

ABSTRACT

An apparatus for cone beam computed tomography can include a support structure, a scanner assembly coupled to the support structure for controlled movement in at least x, y and z orientations, the scanner assembly can include a DR detector configured to move along at least a portion of detector path that extends at least partially around a scan volume with a distance D 1  that is sufficiently long to allow the scan volume to be positioned within the detector path; a radiation source configured to move along at least a portion of a source path outside the detector path, the source path having a distance D 2  greater than the distance D 1,  the distance D 2  being sufficiently long to allow adequate radiation exposure of the scan volume for an image

FIELD OF THE INVENTION

The invention relates generally to diagnostic imaging and in particularto cone beam imaging systems used for obtaining volume images ofextremities.

BACKGROUND OF THE INVENTION

3-D volume imaging has proved to be a valuable diagnostic tool thatoffers significant advantages over earlier 2-D radiographic imagingtechniques for evaluating the condition of internal structures andorgans. 3-D imaging of a patient or other subject has been made possibleby a number of advancements, including the development of high-speedimaging detectors, such as digital radiography (DR) detectors thatenable multiple images to be taken in rapid succession.

Cone beam computed tomography (CBCT) or cone beam CT technology offersconsiderable promise as one type of diagnostic tool for providing 3-Dvolume images. Cone beam CT systems capture volumetric data sets byusing a high frame rate digital radiography (DR) detector and an x-raysource, typically affixed to a gantry that rotates about the object tobe imaged, directing, from various points along its orbit around thesubject, a divergent cone beam of x-rays toward the subject. The CBCTsystem captures projections throughout the rotation, for example, one2-D projection image at every degree of rotation. The projections arethen reconstructed into a 3D volume image using various techniques.Among well known methods for reconstructing the 3-D volume image fromthe 2-D image data are filtered back projection approaches.

Although 3-D images of diagnostic quality can be generated using CBCTsystems and technology, a number of technical challenges remain. In somecases, for example, there can be a limited range of angular rotation ofthe x-ray source and detector with respect to the subject. CBCT Imagingof legs, arms, and other extremities can be hampered by physicalobstruction from a paired extremity. This is an obstacle that isencountered in obtaining CBCT image projections for the human leg orknee, for example. Not all imaging positions around the knee areaccessible; the patient's own anatomy often prevents the radiationsource and image detector from being positioned over a portion of thescan circumference.

To illustrate the problem faced in CBCT imaging of the knee, the topview of FIG. 1 shows the circular scan paths for a radiation source 22and detector 24 when imaging the right knee R of a patient as a subject20. Various positions of radiation source 22 and detector 24 are shownin dashed line form. Source 22, placed at some distance from the knee,can be positioned at different points over an arc of about 200 degrees;with any larger arc the paired extremity, left knee L, blocks the way.Detector 24, smaller than source 22 and typically placed very nearsubject 20, can be positioned between the patient's right and left kneesand is thus capable of positioning over the full circular orbit.

A full 360 degree orbit of the source and detector is not needed forconventional CBCT imaging; instead, sufficient information for imagereconstruction can be obtained with an orbital scan range that justexceeds 180 degrees by the angle of the cone beam itself, for example.However, in some cases it can be difficult to obtain much more thanabout 180 degree revolution for imaging the knee or other joints andother applications. Moreover, there can be diagnostic situations inwhich obtaining projection images over a certain range of angles hasadvantages, but patient anatomy blocks the source, detector, or bothfrom imaging over that range. Some of the proposed solutions forobtaining images of extremities under these conditions require thepatient to assume a position that is awkward or uncomfortable. Theposition of the extremity, as imaged, is not representative of how thelimb or other extremity serves the patient in movement or underweight-bearing conditions. It can be helpful, for example, to examinethe condition of a knee or ankle joint under the normal weight loadexerted on that joint by the patient as well as in a relaxed position.But, if the patient is required to assume a position that is not usuallyencountered in typical movement or posture, there may be excessivestrain, or insufficient strain, or poorly directed strain or tension, onthe joint. The knee or ankle joint, under some artificially applied loadand at an angle not taken when standing, may not behave exactly as itdoes when bearing the patient's weight in a standing position. Images ofextremities under these conditions may fail to accurately represent howan extremity or joint is used and may not provide sufficient informationfor assessment and treatment planning.

Still other difficulties with conventional solutions for extremityimaging relate to poor image quality. For image quality, the CBCTsequence requires that the detector be positioned close to the subjectand that the source of the cone beam radiation be at a sufficientdistance from the subject. This provides the best image and reducesimage truncation and consequent lost data. Positioning the subjectmidway between the detector and the source, as some conventional systemshave done, not only noticeably compromises image quality, but alsoplaces the patient too near the radiation source, so that radiationlevels are considerably higher.

CBCT imaging represents a number of challenges that also affect othertypes of volume imaging that employ a radiation source and detectororbiting an extremity over a range of angles. There are varioustomographic imaging modes that can be used to obtain depth informationfor a scanned extremity.

In summary, for extremity imaging, particularly for imaging the lowerpaired extremities, a number of improvements are needed, including thefollowing:

-   -   (i) improved placement of the radiation source and detector        relative to the imaged subject to provide acceptable radiation        levels and image quality throughout the scanning sequence, with        the capability for at least coarse automated setup for examining        an extremity under favorable conditions;    -   (ii) system flexibility for imaging at different heights with        respect to the rotational axis of the source and detector,        including the flexibility to allow imaging with the patient        standing or seated comfortably, such as with a foot in an        elevated position, for example;    -   (iii) capability to adjust the angle of the rotational axis to        suit patient positioning requirements;    -   (iv) improved patient accessibility, so that the patient does        not need to contort, twist, or unduly stress limbs or joints        that may have been injured in order to provide images of those        body parts;    -   (v) improved ergonomics for obtaining the CBCT image, allowing        the patient to stand or sit with normal posture, for example.        This would also allow load-bearing extremities, such as legs,        knees, and ankles, to be imaged under the normal load exerted by        the patient's weight, rather than under simulated loading        conditions and provide options for supporting the patient; and    -   (vi) adaptability for multi-use imaging, allowing a single        imaging apparatus to be configurable for imaging any of a number        of extremities, including knee, ankle, toe, hand, elbow, and        other extremities. This also includes the capability to operate        the imaging system in different imaging modes, including CBCT,        two-dimensional (2-D) projection radiography, fluoroscopy, and        other tomography modes.

In summary, the capability for straightforward configuration andpositioning of the imaging apparatus allows the advantages of CBCTimaging to be adaptable for use with a range of extremities, to obtainvolume images under a suitable imaging modality, with the imageextremity presented at a suitable orientation under both load-bearingand non-load-bearing conditions, and with the patient appropriatelystanding or seated.

SUMMARY OF THE INVENTION

An aspect of this application is to advance the art of medical digitalradiography.

Another aspect of this application is to address, in whole or in part,at least the foregoing and other deficiencies in the related art.

It is another aspect of this application to provide, in whole or inpart, at least the advantages described herein.

It is another aspect of this application to advance the art ofdiagnostic imaging of extremity body parts, particularly jointed orload-bearing, paired extremities such as knees, legs, ankles, fingers,hands, wrists, elbows, arms, and shoulders.

It is another aspect of this application to provide apparatus and/ormethod embodiments that adapt to imaging conditions suitable for a rangeof extremities and/or allows the patient to be in a number of positionsfor suitable imaging of the extremity.

It is another aspect of this application to provide apparatus and/ormethod embodiments that provide a radiation source actuator that isoperable independently of a detector actuator within a scanner housingfor a CBCT imaging apparatus.

It is another aspect of this application to provide apparatus and/ormethod embodiments that provide radiation absorbent shielding to atleast portions of surfaces of the housing or a door for absorbingradiation during exposure for a CBCT imaging apparatus.

It is another aspect of this application to provide apparatus and/ormethod embodiments that provide a first mode of the imaging apparatus toperform CBCT imaging of a scan volume and a second mode of the imagingapparatus to perform tomography imaging of the scan volume for a CBCTimaging apparatus.

From one aspect, the present invention provides an apparatus for conebeam computed tomography that can include a support structure; a scannerassembly coupled to the support structure that can include a digitalradiation detector, the detector configured to move along at least aportion of a detector path, the at least a portion of the detector pathextending so that the detector is configured to move at least partiallyaround a scan volume, the detector path having a distance D1 that issufficiently long to allow the scan volume to be positioned within thedetector path; a radiation source, the source configured to move alongat least a portion of a source path outside the detector path, thesource path having a distance D2 greater than the distance D1, thedistance D2 being sufficiently long to allow adequate radiation exposureof the scan volume for an image capture by the detector; a gap in thedetector path and the source path to provide radial access to the scanvolume; and a control panel coupled to the support structure to providean operator interface for entering instructions for operation of theapparatus. In one embodiment, a first mode of the imaging apparatusperforms CBCT imaging of the scan volume and a second mode of theimaging apparatus performs tomography imaging of the scan volume.

These objects are given only by way of illustrative example, and suchobjects may be exemplary of one or more embodiments of the invention.Other desirable objectives and advantages inherently achieved by thedisclosed invention may occur or become apparent to those skilled in theart. The invention is defined by the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features, and advantages of theinvention will be apparent from the following more particulardescription of the embodiments of the invention, as illustrated in theaccompanying drawings. The elements of the drawings are not necessarilyto scale relative to each other.

FIG. 1 is a schematic view showing the geometry and limitations of CBCTscanning for portions of the lower leg.

FIG. 2 shows a top and perspective view of the scanning pattern for animaging apparatus according to an embodiment of the application.

FIG. 3A is a perspective view showing patient access to an imagingapparatus according to an embodiment of the application.

FIG. 3B is a top view showing a sequence of steps for enclosing theextremity to be imaged within the path of the detector transport.

FIG. 4 show portions of the operational sequence for obtaining CBCTprojections of a portion of a patient's leg at a number of angularpositions when using the imaging apparatus according to an embodiment ofthe application.

FIG. 5 is a perspective view that shows a CBCT imaging apparatus forextremity imaging according to an embodiment of the application.

FIG. 6A shows internal components used for imaging ring translation andpositioning.

FIG. 6B shows reference axes for rotation and translation.

FIG. 6C is a schematic diagram that shows components of the positioningsystem for the imaging scanner.

FIG. 6D is a perspective view showing some of the components of avertical translation apparatus.

FIG. 6E shows the CBCT imaging apparatus with covers installed.

FIG. 7A shows translation of the imaging ring with respect to a verticalor z-axis.

FIG. 7B shows rotation of the imaging ring about an α-axis that isorthogonal to the z-axis.

FIG. 7C shows rotation of the imaging ring about a γ-axis that isorthogonal to the α-axis.

FIG. 7D shows the position of operator controls for fine-tune positionof the imaging scanner.

FIG. 7E shows an enlarged view of the positioning controls.

FIG. 8 is a perspective view that shows the extremity imaging apparatusconfigured for knee imaging with a standing patient.

FIG. 9 is a perspective view that shows the extremity imaging apparatusconfigured for foot or ankle imaging with a standing patient.

FIG. 10 is a perspective view that shows the extremity imaging apparatusconfigured for knee imaging with a seated patient.

FIG. 11 is a perspective view that shows the extremity imaging apparatusconfigured for foot or ankle imaging with a seated patient.

FIG. 12 is a perspective view that shows the extremity imaging apparatusconfigured for toe imaging with a seated patient.

FIG. 13 is a perspective view that shows the extremity imaging apparatusconfigured for hand imaging with a seated patient.

FIG. 14 is a perspective view that shows the extremity imaging apparatusconfigured for elbow imaging with a seated patient.

FIG. 15A is a top view of the scanner components of an extremity imagingapparatus according to an embodiment of the application.

FIG. 15B is a perspective view of a frame that supports scannercomponents of an extremity imaging apparatus according to an embodimentof the application.

FIG. 15C is a perspective view of a frame that supports scannercomponents of an extremity imaging apparatus with added counterweightaccording to an embodiment of the application.

FIG. 16A is a top view of the imaging scanner showing the door openposition.

FIG. 16B is a perspective view of the imaging scanner showing a doorclosing position.

FIG. 16C is a top view of the imaging scanner showing the door closedposition.

FIG. 16D is a perspective view showing the door in closed position.

FIG. 17A is a top view of the imaging scanner with a number of itsinternal imaging components shown, at one extreme end of the imagingscan.

FIG. 17B is a top view of the imaging scanner with a number of itsinternal imaging components shown, at the opposite extreme end of theimaging scan from that shown in FIG. 17A.

FIG. 17C is a top view of the imaging scanner with its housing shown.

FIG. 17D is a top view of the imaging scanner with internal imagingcomponents and central arc angles shown.

FIG. 18 shows partial paths of scanner components within the housing forseparate actuation of the source and detector for orbit about the scanvolume.

FIG. 19 is a top view showing the scanning sequence when using twoseparate actuators for detector and radiation source.

FIG. 20 shows shielding provided for internal components of the scannerhousing.

FIG. 21 shows shielding provided along the gantry, including a backingplate behind the detector.

FIG. 22 is a diagram that shows another exemplary embodiment fortomosynthesis imaging conducted by a CBCT imaging apparatus according toembodiments of the application.

FIG. 23 is a diagram that shows another exemplary embodiment fortomosynthesis imaging conducted by a CBCT imaging apparatus according toembodiments of the application.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The following is a description of exemplary embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

For illustrative purposes, principles of the invention are describedherein by referring mainly to exemplary embodiments thereof. However,one of ordinary skill in the art would readily recognize that the sameprinciples are equally applicable to, and can be implemented in, alltypes of radiographic imaging arrays, various types of radiographicimaging apparatus and/or methods for using the same and that any suchvariations do not depart from the true spirit and scope of theapplication. Moreover, in the following description, references are madeto the accompanying figures, which illustrate specific exemplaryembodiments. Electrical, mechanical, logical and structural changes canbe made to the embodiments without departing from the spirit and scopeof the invention.

In the context of the application, the term “extremity” has its meaningas conventionally understood in diagnostic imaging parlance, referringto knees, legs, ankles, fingers, hands, wrists, elbows, arms, andshoulders and any other anatomical extremity. The term “subject” is usedto describe the extremity of the patient that is imaged, such as the“subject leg”, for example. The term “paired extremity” is used ingeneral to refer to any anatomical extremity wherein normally two ormore are present on the same patient. In the context of the application,the paired extremity is not imaged unless necessary; only the subjectextremity is imaged. In one embodiment, a paired extremity is not imagedto reduce patient dose.

A number of the examples given herein for extemporary embodiments of theapplication focus on imaging of the load-bearing lower extremities ofthe human anatomy, such as the leg, the knee, the ankle, and the foot,for example. However, these examples are considered to be illustrativeand non-limiting.

In the context of the application, the term “arc” or, alternately, orarcuate has a meaning of a portion of a curve, spline or non-linearpath, for example as being a portion of a curve of less than 360 degreesor, considered alternately, of less than 2π radians for a given radiusor distance from a central bore.

The term “actuable” has its conventional meaning, relating to a deviceor component that is capable of effecting an action in response to astimulus, such as in response to an electrical signal, for example.

As used herein, the term “energizable” relates to a device or set ofcomponents that perform an indicated function upon receiving power and,optionally, upon receiving an enabling signal.

In the context of the application, two elements are considered to besubstantially orthogonal if their angular orientations differ from eachother by 90 degrees, +/− no more than about 10 degrees.

It is instructive to observe that the mathematical definition of acylinder includes not only the familiar “can-shaped” right circularcylinder, but also any number of other shapes. The outer surface of acylinder is generated by moving a first straight line element along aclosed curve or other path along a base plane, while maintaining thefirst straight line element parallel to a second, fixed straight linethat extends out from the base plane, wherein the moving first straightline intersects a fixed closed curve or base in the base plane. A cube,for example, is considered to have a cylindrical shape according to thisdefinition. A can-shaped cylinder of revolution, for example, isgenerated when the moving first straight line intersects a circle in thebase plane at a right angle. An object is considered to be substantiallycylindrical when its overall surface shape is approximated by a cylindershape according to this definition, with allowance for standard edgerounding, protruding or recessed mechanical and electrical fasteners,and external mounting features.

Certain exemplary embodiments according to the application address thedifficulties of extremity imaging by providing an imaging apparatus thatdefines coordinated non-linear source and detector paths (e.g., orbital,curved, concentric about a center point), wherein components thatprovide the source and detector paths are configured to allow patientaccess prior to and following imaging and configured to allow thepatient to sit or stand with normal posture during the CBCT imagecapture series. Certain exemplary embodiments provide this capability byusing a detector transport device that has a circumferential accessopening allowing positioning of the extremity, wherein the detectortransport device is revolved about the positioned extremity once it isin place, enclosing (e.g., partially, substantially, fully) theextremity as it is revolved through at least a portion of the scan.

It is instructive to consider dimensional attributes of the human framethat can be considerations for design of CBCT equipment for scanningextremities. For example, an adult human patient of average height in acomfortable standing position has left and right knees generallyanywhere from about 10 to about 35 cm apart. For an adult of averageheight, exceeding about 35-40 cm (14-15.7 inches) between the kneesbecomes increasing less comfortable and out of the range of normalstanding posture. It is instructive to note that this constraint makesit impractical to use conventional gantry solutions for obtaining theneeded 2-D image sequence. For certain exemplary embodiments, either thesource or the detector must be able to pass between the legs of astanding patient for knee CBCT imaging, a capability not available withgantry or other conventional solutions.

The perspective and corresponding top views of FIG. 2 show how thescanning pattern is provided for components of CBCT imaging apparatus 10according to an embodiment of the application. A detector path 28 of asuitable radius R1 from a central axis β provided for a detector deviceby a detector transport 34. A source path 26 of a second, larger radiusR2 is provided for a radiation source by a source transport 32. In oneembodiment, a non-linear source path 26 is greater in length than anon-linear detector path 24. According to an embodiment of theapplication, described in more detail subsequently, the same transportsystem provides both detector transport 34 and source transport 32. Theextremity, subject 20, is preferably substantially centered alongcentral axis β so that central axis β can be considered as a linethrough points in subject 20. In one embodiment, an imaging bore or theCBCT apparatus can include or encompass the central axis β. The limitinggeometry for image capture is due to the arc of source transport 32,blocked by gap 38 (e.g., for patient anatomy, such as by a paired limb),and thus limited typically to less than about 220 degrees, as notedpreviously. The circumferential gap or opening 38 can occupy the spacebetween the endpoints of the arc of source path 26. Gap or opening 38gives space for the patient a place to stand, for example, while one legis being imaged.

Detector path 28 can extend through circumferential gap 38 to allowscanning, since the detector is not necessarily blocked by patientanatomy but can have a travel path at least partially around an imagedextremity that can extend between the standing patient's legs.Embodiments of the present invention allow temporary restriction of thedetector path 28 to allow access for the patient as part of initialpatient positioning. The perspective view in FIG. 2, for example, showsdetector transport 34 rotated to open up circumferential gap 38 so thatit extends from the axis β (e.g., beyond a source path or housing). Withdetector transport 34 translated to the open position shown in FIG. 3A,the patient can freely move in and out of position for imaging. When thepatient is properly in position, detector transport 34 is revolved aboutaxis β by more than 180 degrees; according to an embodiment of theapplication, detector transport 34 is revolved about axis β bysubstantially 200 degrees. This patient access and subsequent adjustmentof detector transport 34 is shown in successive stages in FIG. 3B. Thisorbital movement confines the extremity to be imaged more effectivelyand places detector 24, not visible in FIGS. 2-3B due to the detectortransport 34 housing, in position near subject 20 for obtaining thefirst projection image in sequence. In one embodiment, a detectortransport 34 can include shielding or a door over part of the detectorpath, and/or the gap 38.

Circumferential gap or opening 38 not only allows access for positioningof the subject leg or other extremity, but also allows sufficient spacefor the patient to stand in normal posture during imaging, placing thesubject leg for imaging in the central position along axis β (FIG. 2)and the non-imaged paired leg within the space defined bycircumferential gap 38. Circumferential gap or opening 38 extendsapproximately 180 degrees minus the fan angle (e.g., between ends of thesource path), which is determined by source-detector geometry anddistance. Circumferential gap or opening 38 permits access of theextremity so that it can be centered in position along central axis β.Once the patient's leg or other extremity is in place, detectortransport 34, or a hooded cover or hollow door or other member thatdefines this transport path, can be revolved into position, closing thedetector portion of circumferential gap or opening 38.

By way of example, the top views of FIG. 4 show portions of theoperational sequence for obtaining CBCT projections of a portion of apatient's leg at a number of angular positions when using a CBCT imagingapparatus. The relative positions of radiation source 22 and detector24, which may be concealed under a hood or chassis, as noted earlier,are shown in FIG. 4. The source 22 and detector 24 can be aligned so theradiation source 22 can direct radiation toward the detector 24 (e.g.,diametrically opposite) at each position during the CBCT scan andprojection imaging. The sequence begins at a begin scan position 50,with radiation source 22 and detector 24 at initial positions to obtainan image at a first angle. Then, both radiation source 22 and detector24 revolve about axis β as represented in interim scan positions 52, 54,56, and 58. Imaging terminates at an end scan position 60. As thissequence shows, source 22 and detector 24 are in opposing positionsrelative to subject 20 at each imaging angle. Throughout the scanningcycle, detector 24 is within a short distance D1 of subject 20. Source22 is positioned beyond a longer distance D2 of subject 20. Thepositioning of source 22 and detector 24 components on each path can becarried out by separate actuators, one for each transport path, or by asingle rotatable member, as described in more detail subsequently. Itshould be noted that scanning motion in the opposite direction, that is,clockwise with respect to the example shown in FIG. 4, is also possible,with the corresponding changes in initial and terminal scan positions.

Given this basic operation sequence in which the source 22 and detector24 orbit the extremity, the usefulness of an imaging system that isadaptable for imaging patient extremities with the patient sitting orstanding and in load-bearing or non load-bearing postures can beappreciated. The perspective view of FIG. 5 shows a CBCT imagingapparatus 100 for extremity imaging according to an embodiment of theapplication. Imaging apparatus 100 has a gimballed imaging ring orscanner 110 that houses and conceals source 22 and detector 24 within ahousing 78. FIG. 5 shows their supporting transport mechanisms. Scanner110 is adjustable in height and rotatable in gimbaled fashion aboutnon-parallel axes, such as about substantially orthogonal axes asdescribed in subsequent figures, to adapt to various patient posturesand extremity imaging conditions. A support column 120 supports scanner110 on a yoke, or bifurcated or forked support arm 130, a rigidsupporting element that has adjustable height and further providesrotation of scanner 110 as described subsequently. Support column 120can be fixed in position, such as mounted to a floor, wall, or ceiling.According to portable CBCT embodiments such as shown in FIGS. 6A andelsewhere, support column 120 mounts to a support base 121 that alsoincludes optional wheels or casters 122 for transporting and maneuveringimaging apparatus 100 into position. A control panel 124 can provide anoperator interface, such as a display monitor, for entering instructionsfor apparatus 100 adjustment and operation. Support column 120 can be offixed height or may have telescoping operation, such as for improvedvisibility when apparatus 100 is moved.

Vertical and Rotational Movement

FIG. 6A shows portions of exemplary internal imaging and positioningmechanisms (with covers removed) for scanner 110 that allow imagingapparatus 100 the capability for imaging extremities with a variety ofconfigurations. FIG. 6B shows rotation axes definitions for scanner 110positioning. The α-axis and the γ-axis are non-parallel, to allowgimbaled action. According to an embodiment of the applications shown inFIG. 6A, the α-axis and the γ-axis are mutually orthogonal. The α-axisis substantially orthogonal to the z-axis. The intersection of theα-axis and the γ-axis can be offset from support column 120 by somenon-zero distance.

First considering the z-axis, FIG. 6A shows an exemplary embodiment toachieve vertical motion. Within support column 120, a vertical carriagetranslation element 128 is actuated in order to travel upwards ordownwards along column 120 within a track 112 in a vertical direction.Carriage translation element 128 has a support shaft 132 that is coupledto an actuator 136 for providing α-axis rotation to forked or C-shapedsupport arm 130. Forked support arm 130, shown only partially in FIG. 6Ato allow a better view of underlying components, is coupled to supportshaft 132. X-ray source 22 and receiver 24 are mounted on a rotatablegantry 36 for rotation about a scan or central axis, designated as the βaxis. Axis β is orthogonal to the α-axis and the γ-axis.

It can be appreciated that z-axis translation can be effected in anumber of ways. Challenges that must be addressed by the type of systemthat is used include handling the weight of forked support arm 130 andthe imaging scanner 110 that arm 130 supports. This can easily weigh afew hundred pounds. In addition, precautions must be provided forhandling conditions such as power loss, contact with the patient, ormechanical problems that hamper positioning movement or operation.According to an embodiment of the application, as shown schematically inFIG. 6C and in the perspective view of FIG. 6D, a vertical actuator 129rotates a threaded shaft 123. Vertical carriage translation element 128employs a ball screw mount apparatus 125 to translate rotational motionto the needed linear (e.g., z-direction) motion, thus urging verticalcarriage translation element 128 upward or allowing vertical carriagetranslation element 128 to move downward. Ball screw translation devicesare advantaged for handling high weight loads and are typically moreefficient than other types of translators using threaded devices. Theuse of a ball screw arrangement also allows a small motor to drive theshaft that lifts scanner 110 into position and can help to eliminate theneed for a complex and bulky counterweight system for allowing controlof vertical movement. An encoder 145, such as a linear encoder element,can provide feedback signals that are used to indicate the verticalposition of vertical carriage translation element 128.

Vertical carriage translation element 128 travels inside track 112formed in support column 120 (FIG. 6A); wheels 138 help to guidetranslation element 128 within the slots. Paired wheels 138 can beorthogonal to each other to provide centering within column 120.

A braking system can also be provided for support column 120.Spring-loaded brakes 142 (FIG. 6D) are positioned to actuate and gripshaft 123 or other mechanical support when mechanical difficulties,power failure, or other conditions are detected. A sensor 144, such as aload cell, is configured to sense rapid movement or interferenceconditions that are undesirable and to cause brake 142 actuation.

Other features of support column 120 for vertical translation includebuilt-in redundancy, with springs to absorb weight and impact, the loadcell to sense a mechanical problem including obstruction by the patient,and manually operable brake mechanisms.

It should be noted that other types of translation apparatus could beused for providing vertical movement of vertical carriage translationelement 128. One conventional method for vertical movement control usesa system of pulleys and counterweights to provide lifting force, withmotorized assistance. Such an arrangement, however, can bedisadvantageous because it can add considerable weight to the column 120and supporting structure. In spite of its weight-related drawbacks, useof a pulley mechanism can be advantageous for allowing a retractable ortelescoping column 120 arrangement, for example, to simplify transportof imaging apparatus 100 between rooms.

Gimbaled Arrangement for Scanner

Forked support arm 130 can support scanner 110 in a gimbaledarrangement. Source 22 and detector 24 are shown on gantry 36 forreference in FIG. 6A and covered in the alternate view of FIG. 6E.Vertical carriage translation element 128 is configured to ride within atrack 112 (FIG. 6A) within support column 120.

For certain exemplary embodiments, some level of manual operability canbe provided, such as for power loss situations. In one embodiment,forked support arm 130 can be lifted upwards in position by one or morepersons, for example, raising vertical carriage translation element 128even when brakes 142 are set. Shifting support arm 130 upwards does notrelease the brakes 142, but simply sets the brakes 142 to hold element128 position at new levels.

According to an alternate embodiment of the application, verticalcarriage translation element 128 can be a motor that moves verticallyalong supporting threaded shaft 132; alternately, vertical carriagetranslation element 128 can be driven using a chain, pulley, or otherintermediate mechanism that has considerable counterweights for manuallyraising and lowering vertical carriage translation element 128 and itsconnected forked support arm 130 and components within support column120. Additional supporting components include a more complex brakingsystem, such as a pneumatic braking system for providing a forceopposing gravity in order to prevent sudden movement of forked supportarm 130 as a precaution against damage or injury. Vertical carriagetranslation element 128 can be automated or may be a manually operatedpositioning device that uses one or more springs or counterweightdevices to allow ease of manual movement of forked support arm 130 intoposition.

Next, considering the α-axis movement of forked support arm 130, in oneembodiment a rotational actuator 136 can be energizable to allowrotation of shaft 132 (FIG. 6A). This rotational actuation can beconcurrent with z-axis translation as well as with rotation with respectto the γ-axis.

Forked support arm 130 allows movement relative to the γ-axis accordingto the position and angle of forked support arm 130. In the example ofFIG. 6A, the γ-axis is oriented vertically, substantially in parallelwith the z-axis. FIG. 6E shows the γ-axis oriented horizontally. Apivoting mount 140 with a rotational actuator 146, provided by forkedsupport arm 130, allows rotation along the γ-axis. The gimbaledcombination of α-axis and γ-axis rotation can allow the imagingapparatus to be set up for imaging in a number of possible positions,with the patient standing, seated, or prone.

An exemplary positioning capability of the imaging apparatus 100 isshown n FIGS. 7A-7C. FIG. 7A shows movement of forked support arm 130 onsupport column 120 to provide z-axis (vertical) translation of scanner110. FIG. 7B shows rotation of forked support arm 130 about thehorizontal α-axis. FIG. 7C shows rotation about the γ-axis as defined bythe C-arm arrangement of forked support arm 130.

Sequence and Controls for Positioning Support Arm 130

According to an embodiment of the present invention, an initial set ofoperator commands automatically configure CBCT imaging apparatus 100 toone of a well-defined set of default positions for imaging, such asthose described subsequently. The patient waits until this initial setupis completed. Then, the patient is positioned at CBCT imaging apparatus100 and any needed adjustments in height (z—axis) or rotation about theα or γ axes can be made by the technician. This type of fine-tuningadjustment is at slow speeds for increased patient comfort and becauseonly incremental changes to position are needed in most cases.

FIG. 7D and the enlarged view of FIG. 7E show user control stations 156,158 that are provided on arm 130 (with scanner 110 removed for improvedvisibility) for operator adjustment of z-axis translation and α-andγ-axis rotation as described in FIGS. 7A-7C. Both control stations 156and 158 are essentially the same, duplicated to allow easier access forthe operator for different extremity imaging arrangements. By way ofexample, FIG. 7E shows an enlarged view of control station 158. Anenablement switch 159 is pressed to activate a control 160 and anassociated indicator illuminates when control 160 is active or enabled.As a patient safety feature to protect from inadvertent patient contactwith the controls in some imaging configurations, one or both controlstations 156, 158 are disabled. One or both control stations 156, 158can also be disabled following a time-out period after switch 159 hasbeen pressed. An emergency stop control 162 can stop all motion of theimaging apparatus including downward motion of support arm 130.

Still referring to FIG. 7E, control 160 can activate any of theappropriate actuators for z-axis translation, α-axis rotation and/orγ-axis rotation. Exemplary responses of the system can be based onoperator action, as follows:

-   -   (i) z-axis vertical movement is effected by pressing control 160        in a vertical upward or downward direction. The control logic        adjusts for the angular position of the support arm 130, so that        pressing the control upward provides z-axis movement regardless        of support arm 130 orientation.    -   (ii) α-axis rotation is effected by rotating control 160.        Circular motion of control 60 in an either clockwise (CW) or        counterclockwise (CCW) direction causes corresponding rotation        about the α axis.    -   (iii) γ-axis rotation is effected by horizontal left-to-right or        right-to-left movement of control 60. As with z-axis movement,        control logic adjusts for the angular position of the support        arm 130, so that left-right or right-left movement is relative        to the operator regardless of support arm 130 orientation.

It should be noted that CBCT imaging apparatus 100 as shown in FIG. 6Eprovides three degrees of freedom (DOF) for scanner 110 positioning. Inaddition to the z-axis translation and rotation about α-and γ-axespreviously described, casters 122 allow rotation of scanner 110 positionwith respect to the z-axis as well as translation along the floor.

Configurations for Imaging Various Extremities

Given the basic structure described with reference to FIGS. 6A-7D, thepositioning versatility of scanner 110 for various purposes can beappreciated. Subsequent FIGS. 8—14 show, by way of example, how thisarrangement serves different configurations for extremity imaging.

FIG. 8 shows an exemplary scanner 110 positioning for a knee exam, wheresubject 20 is a standing patient. An optional patient support bar 150can be attached to support column 120. In one embodiment, support bar150 is mounted to vertical carriage translation element 128.Accordingly, as the vertical carriage translation element 128 moves, acorresponding position of the support bar 150 can be moved. According toan alternate embodiment of the application, the support bar 150 can bemounted to the scanner 110, such as to the cover of scanner 110 or tothe forked support arm 130. In contrast, embodiments of support bar 150can be motionless during imaging or during a scan by the scanner 110.For this embodiment, vertical adjustment along the z-axis sets the kneeof the patient at the center of the scanner 110. Forked support arm 130is arranged so that the plane that contains both the α-axis and theγ-axis is substantially horizontal. Patient access is through anopening, circumferential gap or opening 38 in scanner 110. A door 160 ispivoted into place across gap 38 to enclose an inner portion ofcircumferential gap or opening 38. Door 160 fits between the legs of thepatient once the knee of the patient is positioned.

Certain exemplary embodiments of optional patient support bar 150 can bemounted to movable portions of the CBCT apparatus 100, preferably tohave a prescribed spatial relationship to an imaging volume. For suchembodiments, a presence detector 151 can be configured to detect whenthe support bar 150 is mounted to the CBCT system 100. When detected, acontroller or the like, for example, in the control panel 124, cancalculate scanner 110, and/or forked support arm 130 movements toprevent collisions therebetween with the affixed support bar 150. Thus,when attached support bar 150 can limit motion of the scanner 110.Exemplary presence detectors 151 can include but are not limited tomagnetic detectors, optical detectors, electro-mechanical detectors orthe like. As shown in FIG. 9, a pair of optional or removable supportarms 150 can be affixed to the vertical carriage translation element 128and have their attachment reported by a pair of presence detectors 151.

For FIG. 8 and selected subsequent embodiments, door 160, once pivotedinto its closed position, can effectively extend the imaging path byprotecting and/or providing the curved detector transport 34 path asshown in FIG. 4. With this arrangement, when door 160 is closed toprotect the transport path, the knee can be examined underweight-bearing or non-weight-bearing conditions. By enclosing theportion of detector transport 34 path that crosses opening 38, door 160enables the extremity to be positioned suitably for 3D imaging and to bemaintained in position between the source and detector as these imagingcomponents orbit the extremity in the CBCT image capture sequence.

FIG. 9 shows scanner 110 positioning for a foot or ankle exam whereinsubject 20 is a standing patient. With this configuration, scanner 110is lowered to more effectively scan the area of interest. The plane thatcontains both the α-axis and the γ-axis is approximately 10 degreesoffset from horizontal, rotated about the γ axis. A step 116 is providedacross circumferential gap or opening 38 for patient access.

FIG. 10 shows scanner 110 positioning for a knee exam with the patientseated. For this configuration, forked support arm 130 is elevated withrespect to the z-axis. Rotation about the α-axis orients the γ-axis sothat it is vertical or nearly vertical. Circumferential gap or opening38 is positioned to allow easy patient access for imaging the rightknee. It should be noted that 180 degree rotation about the γ-axis wouldposition circumferential gap or opening 38 on the other side of scanner110 and allow imaging of the other (left) knee.

FIG. 11 shows scanner 110 positioning for a foot or ankle exam with thepatient seated. For this configuration, forked support arm 130 iselevated with respect to the z-axis. Some slight rotation about theα-axis may be useful. Rotation about the γ-axis orients scanner 110 at asuitable angle for imaging. Circumferential gap or opening 38 ispositioned for comfortable patient access.

FIG. 12 shows scanner 110 positioning for a toe exam with the patientseated. For this configuration, forked support arm 130 is elevated withrespect to the z-axis. Rotation about the γ-axis positionscircumferential gap 38 at the top of the unit for patient access.

FIG. 13 shows scanner 110 positioning for a hand exam, with the patientseated. For this configuration, forked support arm 130 is elevated withrespect to the z-axis. Rotation about the γ-axis positionscircumferential gap 38 suitably for patient access. Rotation about thecc-axis may be provided to orient scanner 110 for patient comfort.

FIG. 14 shows scanner 110 positioning for an elbow exam, with thepatient seated. For this configuration, forked support arm 130 is againelevated with respect to the z-axis. Rotation about the γ-axis positionscircumferential gap 38 suitably for patient access. Further rotationabout the α-axis may be provided for patient comfort.

In one embodiment of CBCT imaging apparatus 100, the operator can firstenter an instruction at the control console or control panel 124 thatspecifies the exam type (e.g., for the configurations shown in FIGS.8-14). The system then automatically adapts the chosen configuration,prior to positioning the patient. Once the patient is in place, manuallycontrolled adjustments to z-axis and α-and γ-axes rotations can be made,as described previously.

Scanner Configuration and Operation

As previously described with reference to FIGS. 1-4, scanner 110 isconfigured to provide suitable travel paths for radiation source 22 anddetector 24 about the extremity that is to be imaged, such as thoseshown in FIGS. 8-14. Scanner 110 operation in such various exemplaryconfigurations can present a number of requirements that can be at leastsomewhat in conflict, including the following:

-   -   (i) Imaging over a large range of angles, preferably over an arc        exceeding 180 degrees plus the fan angle of the radiation        source.    -   (ii) Ease of patient access and extremity positioning for a wide        range of limbs.    -   (iii) Capability to allow both weight-bearing and        non-weight-bearing postures that allow imaging with minimized        strain on the patient.    -   (iii) Enclosure to prevent inadvertent patient contact with        moving parts.    -   (iv) Fixed registration of source to detector throughout the        scan cycle.

The top view of FIG. 15A shows a configuration of components of scanner110 that orbit subject 20 according to an embodiment of the application.One or more sources 22 and detector 24 are mounted in a cantileveredC-shaped gantry 36 that is part of a transport assembly 170 that can becontrollably revolved (e.g., rotatable over an arc about central axisβ). Source 22 and detector 24 are thus fixed relative to each otherthroughout their movement cycle. An actuator 172 is mounted to a frame174 of assembly 170 and provides a moving hinge for gantry pivoting.Actuator 172 is energizable to move gantry 36 and frame 174 withclockwise (CW) or counterclockwise (CCW) rotation as needed for the scansequence. Housing 184 can reduce or keeps out dust and debris and/orbetter protect the operator and patient from contact with moving parts.

The perspective view of FIG. 15B shows frame 174 and gantry 36 oftransport assembly 170 in added detail. Actuator 172 cooperates with abelt 178 to pivot frame 174 for moving source 22 and detector 24 aboutaxis β. The perspective view of FIG. 15C shows frame 174 with addedcounterweights 182 for improved balance of the cantilevered arrangement.

Because a portion of the scan arc that is detector path 28 (FIG. 2)passes through the circumferential gap or opening 38 that allows patientaccess, this portion of the scan path should be isolated from thepatient. FIGS. 16A, 16B, and 16C show, in successive positions forclosing over gap or opening 38, a slidable door 176 that is stored in aretracted position within a housing 180 for providing a covering overthe detector path 28 once the patient is in proper position. In oneembodiment, door 176 can be substantially a hollow structure that, whenclosed, allows passage of the detector 24 around the patient'sextremity. Referring to FIG. 15B, the portion of frame 174 of gantry 36that supports detector 24 can pass through the hollow inner chamberprovided by door 176 during the imaging scan. At the conclusion of theimaging sequence, frame 174 of gantry 36 rotates back into its homeposition and door 176 is retracted to its original position for patientaccess or egress within housing 180. In one embodiment, the door 176 ismanually opened and closed by the operator. In one embodiment,interlocks are provided so that movement of scanning transportcomponents (rotation of cantilevered frame 174) is only possible whilefull closure of the door 176 is sensed.

FIG. 16B also shows top and bottom surfaces 190 and 192, respectively,of housing 180. An outer circumferential surface 194 extends between andconnects top and bottom surfaces 190 and 192. An inner circumferentialsurface 196 is configured to connect the top and bottom surfaces 190 and192 to form a central opening 198 extending from the first surface tothe second surface, where the central opening 198 surrounds the βaxis.

As shown with respect to FIGS. 2 and 4, in one embodiment radiationsource 22 and detector 24 each can orbit the subject along an arc withradii R2 and R1, respectively. According to an alternate embodiment,within source transport 32, a source actuator could be used, cooperatingwith a separate, complementary detector actuator that is part ofdetector transport 34. Thus, two independent actuator devices, one ineach transport assembly, can be separately controlled and coordinated byan external logic controller to move source 22 and detector 24 alongtheir respective arcs, in unison, about subject 20.

In the context of the present disclosure, a surface is considered to be“substantially” flat if it has a radius of curvature that exceeds about10 feet.

The perspective view of FIG. 10 shows the extremity CBCT imagingapparatus 100 configured for knee imaging with a seated patient. FromFIG. 10, it can be seen that the patient needs room outside of the scanvolume for comfortable placement of the leg that is not being imaged.For this purpose, housing 78 is shaped to provide additional clearance.

As is readily visible from FIGS. 8-14 and 16A-16D, imaging scanner 110has a housing 78. According to one embodiment of the application,housing 78 is substantially cylindrical; however, a cylindrical surfaceshape for housing 78 is not required. By substantially cylindrical ismeant that, to at least a first approximation, the housing 78 surfaceshape closely approximates a cylinder, with some divergence from strictgeometric definition of a cylinder and with a peripherally gap and someadditional features for attachment and component interface that are notin themselves cylindrical.

FIGS. 17A-17D show a number of features that are of interest for anunderstanding of how scanner 110 is configured and operated (e.g.,scans). FIG. 17A shows how peripheral gap 38 is formed by housing 78,according to an embodiment of the application. Scan volume 228, outlinedwith a dashed line, is defined by the source and detector paths 26 and28, as described previously, and typically includes at least a portionof the β axis. An inner central volume 230 can be defined by surface S2of housing 78 and can typically enclose scan volume 228. Inner centralvolume 230 can also be defined by door 176 when closed, as shown in FIG.17C. Peripheral gap 38 is contiguous with inner central volume 230 whendoor 176 is in open position (e.g., fully or partially opened).

FIG. 17A shows source transport 32 and detector transport 34 at oneextreme end of the scan path, which may be at either the beginning orthe end of the scan. FIG. 17B shows source transport 32 and detectortransport 34 at the other extreme end of the scan path. It should benoted that source 22 is offset along source transport 32. With thisasymmetry, the extent of travel of source 22 relative to surface S3 ofhousing 78 differs from its extent of travel relative to surface S4. Atthe extreme travel position shown in FIG. 17B, source 22 is more thantwice the distance from surface S4 as source 22 is from surface S3 atthe other extreme travel position shown in FIG. 17A. In one embodiment,the inventors use this difference to gain additional clearance forpatient positioning with the patient seated.

FIG. 17C shows the configuration of housing 78. In the context of thepresent disclosure, top surface 190 is considered to be aligned with thetop of, at least partially above, or above scan volume 228; bottomsurface 192 is aligned with the bottom of, at least partially below, orbelow scan volume 228. In one embodiment, the top surface 190 or thebottom surface 192 can intersect a portion of the scan volume 228. Asshown in FIG. 17C, scan volume 228 can be cylindrical or circularlycylindrical. However, exemplary embodiments of the application areintended to be used with other known 2D scan areas and/or 3D scanvolumes. The cover of housing 78 can be metal, fiberglass, plastic, orother suitable material. According to an embodiment, at least portionsof top and bottom surfaces 190 and 192 are substantially flat.

As shown in FIGS. 17A-17C, the scanner 110 has a number of surfaces thatdefine its shape and the shape of peripheral gap or opening 38:

-   -   (i) an outer connecting surface S1 extends between a portion of        top surface 190 and a portion of bottom surface 192 to at least        partially encompass the source and detector; at least a portion        of the outer connecting surface extends outside the path the        source travels while scanning; embodiments of the outer        connecting surface S1 shown in FIGS. 17A-17C provide an arcuate        surface that is generally circular at a radius R5 about center β        and that extends, between edges E1 and E2 of the housing;    -   (ii) an inner connecting surface S2 extends between a portion of        the first surface and a portion of the second surface to define        an inner central volume 230 that includes a portion of scan        volume 228; in the embodiment shown in FIG. 17D, inner        connecting surface S2 is approximately at a radius R4 from the β        axis. At least portions of inner connecting surface S2 can be        cylindrical.    -   (iii) other connecting surfaces can optionally include a surface        S3 that corresponds to a first endpoint of the travel path for        source transport 32 (FIGS. 17A-17B) and is adjacent to curved        surface S1 along an edge E1, wherein surface S3 extends inward        toward curved inner surface S2; and a surface S4 that        corresponds to a second endpoint at the extreme opposite end of        the travel path from the first endpoint for source transport 32        and is adjacent to curved surface S1 along an edge E2 wherein        surface S4 extends inward toward curved inner surface S2.        According to an embodiment, surfaces S3 and S4 are substantially        flat and the angle between surfaces S3 and S4 is greater than        about 90 degrees. In general, other additional surface segments        (e.g., short linear or curved surface segments) may extend        between or comprise any of surfaces S1-S4.

Inner and outer connecting surfaces S1, S2, and, optionally, othersurfaces, define peripheral gap or opening 38 that is contiguous withthe inner central volume 230 and extends outward to intersect the outerconnecting surface S1 to form gap 38 as an angular recess extending frombeyond or toward where the outer connecting surface S1 would, ifextended, cross the opening 38. As shown in FIG. 17D ,a central angle ofa first arc A1 that is defined with a center located within the scanvolume and between edges of the peripheral gap 38 determined at a firstradial distance R4 outside the scan volume is less than a central angleof a second arc A2 that is defined with the first arc center and betweenthe edges of the peripheral gap 38 at a second radial distance R3outside the scan volume, where the second radial distance R3 is greaterthan the first radial distance R4. In one embodiment, as shown in FIG.17D, a first distance that is defined between edges of the peripheralgap 38 determined at a first radial distance R4 outside the scan volumeis less than a second distance between the edges of the peripheral gap38 at a second radial distance R3 outside the scan volume, where thesecond radial distance R3 is greater than the first radial distance R4.According to one embodiment, arcs A1 and A2 are centered about the βaxis, as shown in FIG. 17D and edges of gap 38 are defined, in part, bysurfaces S3 and S4 of housing 78.

The needed room for patient anatomy, such as that described withreference to FIG. 10, can be provided when the central angle for arc A2is large enough to accommodate the extremity that is to be imaged.According to one embodiment, the central angle for arc A2 between edgesof gap 38 exceeds the central angle for arc A1 by at least about 5degrees; more advantageously, the central angle for arc A2 exceeds thecentral angle for arc A1 by at least about 10 or 15 degrees.

The perspective views of FIGS. 8-14 show various configurations ofextremity CBCT imaging apparatus 100 for imaging limbs of a patient. Foreach of these configurations, the limb or other extremity of the patientmust be positioned at the center of scanner 110 and space must beprovided for the paired extremity. As described herein, peripheral gapor opening 38 is provided to allow access space for the patient and roomfor other parts of the patient anatomy. Door 176 is withdrawn into thehousing 78 until the patient is positioned; then, door 176 is pivotedinto place in order to provide a suitable transport path for the imagingreceiver, detector 24, isolated from the patient being imaged.

FIG. 16A shows scanner 110 with door 176 in open position, notobstructing opening 38, that is, keeping opening 38 clear, allowingpatient access for extremity placement within opening 38. FIG. 16C is atop view that shows scanner 110 with door 176 in closed position, heldby a latch 92. Door 176 thus extends into the opening 38, enclosing aportion of opening 38 for imaging of the patient's extremity. A sensor82 provides an interlock signal that indicates at least whether door 176is in closed position or in some other position. Movement of internalscanner 110 components such as c-shaped gantry 36 is prevented unlessthe door 176 is latched shut. A release 90 unlatches door 176 from itslatched position. As shown in FIGS. 16C and 16D, handle 76 can bepositioned outside of opening 38, such as along surface S1 as shown, foropening or closing door 176. Placement of handle 76, or other type ofdoor closure device, outside of opening 38 is advantageous for patientcomfort when closing or opening door 176. As shown in the exemplaryembodiment of FIGS. 16C and 16D, handle 76 is operatively coupled withdoor 176 so that movement of handle 76 in a prescribed direction, suchas along the circumference of scanner 110 housing 78 (e.g., acorresponding direction, or in the clockwise direction shown), causesdoor 176 corresponding movement (e.g., in the same direction). In oneembodiment, clockwise movement of handle 76 causes clockwise movement ofdoor 176, extends door 176 into the opening, and closes door 176;counterclockwise movement of handle 76 causes counterclockwise movementof door 176 and opens door 176, so that it does not obstruct the openingor moves to a position that is clear of the opening.

According to one embodiment, the door 176 is manually pivoted, closed,and opened by the operator. This allows the operator to more carefullysupport the patient and the extremity that is to be imaged. According toan alternate embodiment, an actuator is provided to close or open thedoor automatically.

FIG. 18 shows partial paths of scanner components within housing 78 forseparate actuation of the source 22 and detector 24 for orbit about thescan volume 228 that is centered about the β axis. A radiation sourceactuator 294 translates radiation source 22 along source path 26.Independent of the radiation source 22 movement, a detector actuator 290translates detector 24 along detector path 28. The combined andcoordinated movements of radiation source actuator 294 and detectoractuator 290 cooperate to provide the scan action needed for acquiringthe volume image data from scan volume 228.

FIG. 19 shows a schematic top view of the scanning components of FIG. 18as they orbit the scan volume 228 about the β axis. Scanning begins withcomponents at position 300 and progresses to position 302, position 304,and position 306. In the example shown, coordinated rotation ofactuators 290 and 294 causes orbital movement of source 22 and detector24 about scan volume 228. Source 22 orbits along a radius R2. Detector24 orbits along a shorter radius R1.

Separate actuation for the source 22 and detector 24 components allowsone or the other to be separately moved, which can be convenient forpatient positioning or for storage or transport of the imagingapparatus.

Radiation-absorbent shielding is provided within housing 78 and aboutthe enclosed components in order to help absorb stray and scatteredradiation. As shown in FIG. 20 (with top surface 190 removed forvisibility of internal components), shielding 250 is added to either orboth the inner or outer surfaces of housing 78, including top and bottomsurfaces 190, 192 as well as side surfaces that extend between top andbottom surfaces. Shielding 250 is typically lead or some otherradiation-absorbent material and may be provided in sheet form, fittedagainst and coupled to housing 78. In gantry 36, detector 24 is coupledto a shielded back plate 252 to absorb radiation that might pass throughand around detector 24. Shielding 250 can also be provided on surfacesof door 176, including along closure portion 188.

In the perspective view of gantry 36 given in FIG. 21, it can be seenthat shielding 250 is also provided along straight and curved surfacesthat extend between source 22 and detector 24. In addition, a backingplate 252 provides a shielding function, blocking x-rays from source 22.In position behind detector 24, backing plate 252 also serves as acounterweight to help balance gantry 36 as it rotates through its scancycle. The use of backing plate 252 as counterweight helps to move thecenter of gravity of gantry 36 toward its center of rotation. In oneembodiment, the backing plate can move a center of gravity of thescanner 110 (e.g., source, C-ring, detector) to the beta axis.

It should be noted that, in order to provide a clear path between source22 and detector 24 at all positions of these components during exposure,shielding cannot be provided on surfaces of housing that surround anddefine opening 38. Thus, some additional radiation-absorbent shieldingfor the patient and technician may be helpful for some exam types.

Certain exemplary system and/or method embodiments according to theapplication can provide a tomosynthesis imaging capability. In oneembodiment, the scanner 110 can also support tomosynthesis, which canprovide an image with less rotation than a CT scan. Generally, thesource 22 and the detector 24 travel about 40 degree path while aimingthe scan volume. However, embodiments according to the application canprovide a tomosynthesis imaging capability over a range of 30-80 degreesrelative to a scan volume or patient extremity. In one embodiment, thescanner 110 or system 100 provide the tomosynthesis imaging capabilityor mode in addition to the CBCT imaging capability or mode.

FIG. 22 is a diagram that shows an exemplary embodiment fortomosynthesis imaging conducted by a CBCT imaging apparatus. As shown inFIG. 22, a shoulder of a patient is placed in the scan volume 228 of thescanner 110. In FIG. 22, the patient's body is radially aligned with theperipheral gap 38. In one embodiment, the peripheral gap 38 is onefeature of the scanner 110 that allows the tomosynthesis imagingcapability to be implemented.

FIG. 23 is a diagram that shows another exemplary embodiment fortomosynthesis imaging conducted by a CBCT imaging apparatus. As shown inFIG. 23, a shoulder of a patient is placed in the scan volume 228 of thescanner 110 and the patient's body is aligned parallel to a longitudinalaxis of the scan volume 228 (e.g. the β axis) again in the peripheralgap 38. In one embodiment, the system 100 can be configured to provideat least one of coronal tomography imaging, transverse tomographyimaging and sagittal tomography imaging.

In one embodiment, the door 176 of the scanner 110 can cover a detectorpath through the peripheral gap 38. The door 176 can be in an openposition in the tomosynthesis imaging mode. In an alternativeembodiment, the scanner 110 can include a removable door, to cover thedetector path that is removed in the tomosynthesis imaging mode.

In one embodiment, the tomosynthesis imaging conducted by a CBCT imagingapparatus can use independent source and detector actuators. Forexample, the independent source actuator 294 and detector actuator 290can translate the source 22 and detector 24 using less space in thescanner 110, which can allow for additional movement in the scanner 110or a larger peripheral gap. In another embodiment of the tomosynthesisimaging provided by the CBCT imaging apparatus 100, a subset of CBCTprojection data can be collected during an imaging scan (or selectedfrom the entire set of CBCT projection data) and used to generated 3Dtomography images to reduce metal artifacts.

Consistent with at least one embodiment, exemplary methods/apparatus canuse a computer program with stored instructions that perform on imagedata that is accessed from an electronic memory. As can be appreciatedby those skilled in the image processing arts, a computer program of anembodiment herein can be utilized by a suitable, general-purposecomputer system, such as a personal computer or workstation. However,many other types of computer systems can be used to execute the computerprogram of described exemplary embodiments, including an arrangement ofnetworked processors, for example.

The computer program for performing methods of certain exemplaryembodiments described herein may be stored in a computer readablestorage medium. This medium may comprise, for example; magnetic storagemedia such as a magnetic disk such as a hard drive or removable deviceor magnetic tape; optical storage media such as an optical disc, opticaltape, or machine readable optical encoding; solid state electronicstorage devices such as random access memory (RAM), or read only memory(ROM); or any other physical device or medium employed to store acomputer program. Computer programs for performing exemplary methods ofdescribed embodiments may also be stored on computer readable storagemedium that is connected to the image processor by way of the internetor other network or communication medium. Those skilled in the art willfurther readily recognize that the equivalent of such a computer programproduct may also be constructed in hardware.

It should be noted that the term “memory”, equivalent to“computer-accessible memory” in the context of the present disclosure,can refer to any type of temporary or more enduring data storageworkspace used for storing and operating upon image data and accessibleto a computer system, including a database, for example. The memorycould be non-volatile, using, for example, a long-term storage mediumsuch as magnetic or optical storage. Alternately, the memory could be ofa more volatile nature, using an electronic circuit, such asrandom-access memory (RAM) that is used as a temporary buffer orworkspace by a microprocessor or other control logic processor device.Display data, for example, is typically stored in a temporary storagebuffer that can be directly associated with a display device and isperiodically refreshed as needed in order to provide displayed data.This temporary storage buffer can also be considered to be a memory, asthe term is used in the present disclosure. Memory is also used as thedata workspace for executing and storing intermediate and final resultsof calculations and other processing. Computer-accessible memory can bevolatile, non-volatile, or a hybrid combination of volatile andnon-volatile types.

It will be understood that computer program products for exemplaryembodiments herein may make use of various image manipulation algorithmsand processes that are well known. It will be further understood thatexemplary computer program product embodiments herein may embodyalgorithms and processes not specifically shown or described herein thatare useful for implementation. Such algorithms and processes may includeconventional utilities that are within the ordinary skill of the imageprocessing arts. Additional aspects of such algorithms and systems, andhardware and/or software for producing and otherwise processing theimages or co-operating with the computer program product of theapplication, are not specifically shown or described herein and may beselected from such algorithms, systems, hardware, components andelements known in the art.

It should be noted that while the present description and examples areprimarily directed to radiographic medical imaging of a human or othersubject, embodiments of apparatus and methods of the present applicationcan also be applied to other radiographic imaging applications. Thisincludes applications such as non-destructive testing (NDT), for whichradiographic images may be obtained and provided with differentprocessing treatments in order to accentuate different features of theimaged subject.

Although sometimes described herein with respect to CBCT digitalradiography systems, embodiments of the application are not intended tobe so limited. For example, other DR imaging system such as dental DRimaging systems, mobile DR imaging systems or room-based DR imagingsystems can utilize method and apparatus embodiments according to theapplication. As described herein, an exemplary flat panel DRdetector/imager is capable of both single shot (radiographic) andcontinuous (fluoroscopic) image acquisition. Further, a fan beam CT DRimaging system can be used.

Exemplary DR detectors can be classified into the “direct conversiontype” one for directly converting the radiation to an electronic signaland the “indirect conversion type” one for converting the radiation tofluorescence to convert the fluorescence to an electronic signal. Anindirect conversion type radiographic detector generally includes ascintillator for receiving the radiation to generate fluorescence withthe strength in accordance with the amount of the radiation.

Exemplary embodiments according to the application can include variousfeatures described herein (individually or in combination). Priority isclaimed from commonly assigned, copending U.S. provisional patentapplication Ser. No. 61/710,832, filed Oct. 8, 2012, entitled “ExtremityScanner and Methods For Using The Same”, in the name of John Yorkston etal., the disclosure of which is incorporated by reference.

While the invention has been illustrated with respect to one or moreimplementations, alterations and/or modifications can be made to theillustrated examples without departing from the spirit and scope of theappended claims. In addition, while a particular feature of theinvention can have been disclosed with respect to one of severalimplementations, such feature can be combined with one or more otherfeatures of the other implementations as can be desired and advantageousfor any given or particular function. The term “at least one of” is usedto mean one or more of the listed items can be selected. The term“about” indicates that the value listed can be somewhat altered, as longas the alteration does not result in nonconformance of the process orstructure to the illustrated embodiment. Finally, “exemplary” indicatesthe description is used as an example, rather than implying that it isan ideal. Other embodiments of the invention will be apparent to thoseskilled in the art from consideration of the specification and practiceof the invention disclosed herein. It is intended that the specificationand examples be considered as exemplary only, with a true scope andspirit of the invention being indicated by the following claims.

1. An apparatus for cone beam computed tomography, the apparatuscomprising: a support structure; a scanner assembly coupled to thesupport structure, comprising: a digital radiation detector, thedetector configured to move along at least a portion of a detector path,the at least a portion of the detector path extending so that thedetector is configured to move at least partially around a scan volume,the detector path having a distance D1 that is sufficiently long toallow the scan volume to be positioned within the detector path; aradiation source, the source configured to move along at least a portionof a source path outside the detector path, the source path having adistance D2 greater than the distance D1, the distance D2 beingsufficiently long to allow adequate radiation exposure of the scanvolume for an image capture by the detector; a gap in the detector pathand the source path to provide radial access to the scan volume; and acontrol panel coupled to the support structure to provide an operatorinterface for entering instructions for operation of the apparatus;where a first mode of the imaging apparatus is configured to performCBCT imaging of the scan volume and a second mode of the imagingapparatus is configured to perform tomography imaging of the scanvolume.
 2. The apparatus according to claim 1, where in the secondtomography imaging mode an extremity is longitudinally oriented in thescan volume and gap or the extremity is radially oriented in the scanvolume and the gap.
 3. The apparatus according to claim 1, wherein theradiation source has a radiation source actuator that is operableindependently and separate from a detector actuator to reduce weight. 4.The apparatus according to claim 1, where in the second tomographyimaging mode the source and the detector travel at least a corresponding30 degree path.
 5. The apparatus according to claim 1, where the scannerassembly comprises a retractable door to cover a detector path gap,where in the second tomography imaging mode the door is retracted orwhere the scanner assembly comprises a removable door to cover adetector path gap, where in the second tomography imaging mode the dooris removed from the scanner assembly.
 6. The apparatus according toclaim 1, where in the second tomography imaging mode a subset of theCBCT projections are exposed to generate a topographic imaging data setto reduce metal artifacts.
 7. The apparatus according to claim 1,further comprising: a first device configured to move the scannerassembly along a vertical direction of the support column; a seconddevice configured to revolve the scanner assembly to a vertical or otherangular orientation; and a third device configured to orient the scannerassembly by revolving the scanner assembly about a different axis thatthe second device.
 8. The apparatus according to claim 1, whereinradiation absorbent shielding is added to at least portions of surfacesof the housing or a door for absorbing radiation during exposure,wherein the detector is coupled to a radiation-absorbent backing plate.9. The apparatus according to claim 1, wherein the detector is coupledto a radiation-absorbent backing plate, where the weight of theradiation-absorbent backing plate is configured to position a center ofmass for the gantry is on the beta axis.
 10. An imaging apparatus forcone beam computed tomography imaging of an extremity, the apparatuscomprising a scanner that scans a scan volume about a β axis, thescanner comprising: a) a housing that defines an opening for patientextremity access to the scan volume; b) a detector for acquiring imagedata from the scan volume according to received radiation, wherein thedetector has a detector actuator and is translatable to orbit the scanvolume along a detector path that lies at a first radius R1 about the βaxis; c) a radiation source that is energizable to direct radiationthrough the scan volume and toward the detector, wherein the radiationsource has a radiation source actuator that is operable independently ofthe detector actuator and wherein the radiation source is moveable toorbit the scan volume at a second radius R2 about the β axis.
 11. Theimaging apparatus of claim 1, where the independent operation of theradiation source actuator and the detector actuator operate to positionthe source and the detector in a first relative position before imagingand in a second relative position during imaging.
 12. An apparatus forcone beam computed tomographic imaging of one extremity, the apparatuscomprising: a digital radiation detector; a detector mechanism attachedto the detector and configured to move the detector along a detectorpath, a shape of the detector path comprising a first circular arc, thedetector path defining a detector axis whereat at least a portion of theone extremity is positioned to be imaged by the apparatus; a radiationsource; and a source mechanism separate from the detector mechanism, thesource mechanism attached to the source and configured to move thesource along a source path, the source mechanism controllable to movethe source independent of the detector movement, a shape of the sourcepath comprising a second circular arc, the source path defining a sourceplane and a source axis, the source axis coaxial with the detector axis,wherein a distance from the detector path to the detector axis isshorter than a distance from the source path to the source axis.
 13. Theapparatus of claim 12, wherein the source mechanism and the detectormechanism are configured to position the source and detector,respectively, in a first relative position before imaging, and in asecond relative position while performing imaging.
 14. The apparatus ofclaim 13, wherein the apparatus is configured to position the extremityat the detector axis while the source and detector are disposed in thefirst relative position.
 15. The apparatus of claim 14, wherein theapparatus is configured to image the extremity at the detector axiswhile the source and detector are disposed in the second relativeposition.
 16. The apparatus of claim 13, wherein the source and detectorare diametrically opposite the detector axis in the second relativeposition.
 17. The apparatus of claim 12, wherein the source mechanismincludes a rigid C-shaped assembly to provide mechanical support for thesource as the source is moved along the source path.
 18. The apparatusof claim 17, wherein the detector mechanism includes the rigid C-shapedassembly to provide mechanical support for the detector as the detectoris moved along the detector path.
 19. The apparatus of claim 18, whereinthe source mechanism further includes a source support arm, a proximateend of the source support arm attached to the C-shaped assembly and adistal end of the source support arm attached to the source to providemechanical support for the source as the source is moved along thesource path.
 20. The apparatus of claim 12, further comprising aC-shaped housing to enclose the source and the source mechanism as thesource moves along the source path and to enclose the detector and thedetector mechanism as the detector moves along a portion of the detectorpath.